The move from MobileMe to iCloud saw a number of services dropped that some of us had come to depend on. There's a way to get at least some of them back.

Keychain Sync

On one of your Macs:

mv ~/Library/Keychains ~/Library/Mobile\ Documents/

ln -s ~/Library/Mobile\ Documents/Keychains ~/Library/Keychains

Then on each of the other Macs:

mv ~/Library/Keychains ~/Desktop

ln -s ~/Library/Mobile\ Documents/Keychains ~/Library/Keychains

iDisk / Dropbox

You can of course use this trick to create yourself a little iDisk/Dropbox too:

On one of your Macs:

mkdir ~/Library/Mobile\ Documents/iDisk

ln -s ~/Library/Mobile\ Documents/iDisk ~/iDisk

Then on each of the other Macs:

ln -s ~/Library/Mobile\ Documents/iDisk ~/iDisk

Warning:This isn't actually going to merge multiple changes to your keychain – the latest one modified will prevail – and so if for some reason you deleted it from one Mac (or signed out of iCloud), it would also go on the others. The behaviour is also uncertain if two copies changed simultaneously.

Caveat: Don't blame me if this doesn't work / you lose all of your data / this breaks the ToS for your iCloud account.